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Scientists temporarily attached a pig kidney to a human body and watched it begin to function, a small step in a decades-long quest to one day use animal organs for life-saving transplants.

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Pigs have been the most recent research focus to address organ shortages, but among the odds: A sugar in pig cells, foreign to the human body, causes immediate organ rejection. The kidney for this experiment came from a gene-edited animal that had been engineered to eliminate that sugar and ward off attack by the immune system.

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Surgeons connected the pig’s kidney to a pair of large blood vessels on the outside of the deceased recipient’s body so they could see it for two days. The kidney did what it was supposed to do — filtering out waste and producing urine — and didn’t trigger rejection.

“It was a perfectly normal function,” said Dr. Robert Montgomery, who led the surgical team at NYU Langone Health last month. “It wasn’t this immediate rejection that we’re worried about.”

This research is “an important step forward,” said Dr. Andrew Adams of the University of Minnesota Medical School, who was not part of the work. This will reassure patients, researchers and regulators that “we are moving in the right direction.”

The dream of animal-to-human transplantation – or xenotransplantation – goes back to the 17th century with stumbling attempts to use animal blood for transfusion. By the 20th century, surgeons were attempting to transplant organs from baboons into humans, most notably Baby Fay, a dying infant who lived with a baboon’s heart for 21 days.

With no lasting success and much public uproar, scientists switched from primates to pigs, tampering with their genes to bridge the species gap.

FILE IMAGE – Surgeons are pictured in the background in an operating room. (Photo via Getty Images by Fairfax Media via Getty Images)

Pigs have advantages over monkeys and apes. They are bred for food, so using them for organs poses fewer ethical concerns. Pigs have larger litters, shorter gestation periods, and limbs than humans.

Pig heart valves have also been successfully used in humans for decades. The blood thinner heparin is derived from pig intestines. Pig skin grafts are used on burns and Chinese surgeons have used pig corneas to restore vision.

In the NYU case, researchers put a dead woman’s body on a ventilator after her family agreed to the experiment. The woman wanted to donate her organs, but they were not suitable for traditional donation.

Montgomery said, “The family thought there was a potential for something good to come out of this gift.”

Montgomery himself had received a transplant three years earlier, a human heart from a donor with hepatitis C because he was willing to take any organ. “I was one of those people who waited in the ICU and didn’t know if an organ was going to arrive on time,” he said.

Several biotech companies are racing to develop pig organs suitable for transplantation to help alleviate human organ shortages. More than 90,000 people in the US are in line for kidney transplants. Every day 12 people die while waiting.

The advance is a win for Revvicor, a subsidiary of United Therapeutics, which engineers the pig and its cousins, a herd of 100 raised under tightly controlled conditions at a facility in Iowa.

Pigs lack a gene that produces alpha-gal, the sugar that provokes an immediate attack from the human immune system.

In December, the Food and Drug Administration approved the gene change in Revivicor pigs as safe for human food consumption and medicine.

But the FDA said developers would need to submit more paperwork before pig organs can be transplanted into live humans.

“This is an important step toward realizing the promise of xenotransplantation, which will save thousands of lives each year,” United Therapeutics CEO Martin Rothblatt said in a statement.

Experts say tests on nonhuman primates and last month’s experiments with human bodies pave the way for the first experimental pig kidney or heart transplants in living people over the next several years.

Raising pigs as organ donors seems wrong to some, but it may be more acceptable if concerns about animal welfare can be addressed, said Karen Maschke, a research scholar at the Hastings Center who The first will help develop ethics and policy recommendations. Clinical trial under a grant from the National Institutes of Health.

“There’s going to be a second issue: Should we do this just because we can?” Mashke said.

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